Thanks to Subaru for partnering with us on this SciShow mini series. The all new 2020 Subaru Outback
helped us stay comfortable during filming.
[♪INTRO]
Stefan: Welcome back to Washington! This is the final
episode in our mini-series about the geology of Olympic National Park!
Alexis: So far, we’ve talked about Mt. Olympus and
an ancient that transformed Washington and now, it’s time for one last story.
Stefan, let’s hit the beach!
Stefan: Oh yeah!
Stefan: Last week when we were at Rialto Beach, you
might have noticed a bunch of cool rock towers in the background. Those are called sea stacks,
and these beaches in western Washington are famous for them.
Alexis: But these rocks don’t just look cool. They
also tell a fascinating story about how this landscape has changed over the last few centuries.
Alexis: Welcome to Ruby Beach!
Stefan: We figured that while we were in Washington, we should
visit at least two place that have sea stacks. I mean, like, when in Rome…right?
Alexis: Something like that. Anyway!
Alexis: So, behind us, are some of Ruby Beach’s
famous sea stacks. Sea stacks can be made of all kinds of rock, but the ones here are
generally made of the sedimentary rock breccia and mostly-volcanic conglomerate.
Basically, that means they’re made of a bunch of rocks that got cemented together.
Stefan: Meanwhile, the ones over at Rialto Beach are made
of volcanic basalt, sedimentary sandstone, and conglomerate, depending on
where you look.
Alexis: Exactly what the stacks are made of doesn’t
matter that much, but the important thing to know is that these sea stacks are made
of harder rock than the stuff you tend of finding on the mainland. And that’s important because
of how sea stacks are formed in the first place.
Stefan: Sea stacks form because of something called
preferential erosion.
You start off with a headland, or a piece of the coast that juts out into the ocean.
As the ocean waves come in, they get bent around the headland and end up hitting the
coast in specific spots. And that’s where the trouble starts. Or the fun.
If the area where the waves hit is made of softer rock, or made of a rock that contains
some kind of fracture, the waves will erode it.
That leads to small indents in the headland, and then small caves, and then eventually,
the water cuts straight through. And then you’re left with a sea arch!
Stefan: You can find sea arches all over the place,
but it’s not like erosion stops once that arch is formed. The waves continue to
erode the rock, and over time the arch can get bigger until it eventually collapses into sea stacks.
Alexis: But the rock composition isn’t the only
variable. According to a cool model published in 2014, the beach in front
of the sea stack is important, too.
The model found that really wide beaches tend to prevent sea stacks from forming, because they
act as protective barriers. Basically, the waves crash against the beach and don’t
actually hit the headland.
Meanwhile, really narrow beaches can encourage sea stacks to form. In that case, the water
picks up all the sand and other sediment, and it rubs against the headland kind of like sandpaper.
So erosion happens faster.
Over all, this means that, if Ruby Beach were a lot wider, we might not have these rocks
to look at!
Stefan: So, the sea stacks at Olympic National Park
are really cool, but that's not the only place you can find them.
They're all over the world, from Scotland to Australia. And when you do find them, they can tell you somethings about the place you are visiting.
Alexis: For one, at the most basic level, you can
learn where the coastline used to be. Because anywhere there’s a sea stack — well, that
used to be part of the mainland!
Stefan: Sea stacks also tell you that waves are mainly
approaching the coast head-on, rather than on an angle. When the waves come in sideways,
they erode mostly one side of a headland, and that makes it a lot harder for sea stacks to form.
Alexis: And finally, sea stacks tell you that there’s
a sort of balanced system happening here. Kind of like we talked about in the Mt. Olympus
episode earlier on this trip!
If you find a sea stack, you know there’s a good amount of sediment moving around
and eroding the cliffs, but not so much that it forms a wide protected beach that prevents erosion.
So, generally, when you find a sea stack, there won’t be some kind of huge sprawling
beach stretching way out into the water.
Stefan: Instead, you’re more likely to see something
like this!
Stefan: So while sea stacks are pretty cool, but they won’t
last forever — probably not more than a few hundred years, depending on how big they are
and what they’re made of.
Alexis: They’re a reminder that the land around
you is constantly changing, and that there’s a lot you can learn if you know what to look for.
Stefan: But… there’s one more thing we
should mention about sea stacks. Because while they are really nice to look at, they are
also kind of dangerous.
Alexis: It’s true. Like, in the late 1800s, one
ship near Rialto Beach got caught in some rough waves and foggy weather. Someone on
the board saw a sea stack through the fog and thought it was another boat, so they decided
to steer toward it… and ended up crashing.
Stefan: There have actually been over a hundred
shipwrecks off the coast of Washington, due to sea stacks, rough waters, tons of fog,
and reefs are hiding just under the waves. So while these are nice
to look at during the daytime…
Alexis: We’re going to stick to dry land. And on
that note, we should probably head back to the car and tell Hank we’re about done here!
Stefan: That sounds great! So until next time, thank you
for joining us on our road trip!
Alexis: Thanks to Subaru for partnering with us for this three-part road trip series, and for lending the support of an all-new 2020 Subaru Outback.
Stefan: We had to drive a lot to make these episodes, both
inside Olympic National Park and out, and all the features of the outback help make our trip a lot easier.
My favorite feature was the roomy cargo space! We fit our luggage and even film gear easily.
And with the hands-free power rear gate, I didn’t have to put my bags down on the wet
ground to open the door. Which is always a struggle, right?
Alexis: If you want to learn more about the 2020 Subaru
Outback, you can check out the link in the description.
[ ♪OUTRO ]